[MiscDiagnostics] Look through ABISafe conversions while determining whether access is mutating or not

Otherwise `inout` uses of declarations that require ABI safe conversions
are going to be diagnosed as non-mutating.

(cherry picked from commit ff5e2dd)

Author: xedin

lib/Sema/MiscDiagnostics.cpp

@@ -4333,6 +4333,9 @@ void VarDeclUsageChecker::markStoredOrInOutExpr(Expr *E, unsigned Flags) {
     if (auto *expr = OpaqueValueMap[OVE])
       return markStoredOrInOutExpr(expr, Flags);
 
+  if (auto *ABIConv = dyn_cast<ABISafeConversionExpr>(E))
+    return markStoredOrInOutExpr(ABIConv->getSubExpr(), Flags);
+
   // If we don't know what kind of expression this is, assume it's a reference
   // and mark it as a read.
   E->walk(*this);